What stabilizes this mechanism is a very good question. When I started this exercise, I thought that providing the 6 cylinder lengths will "fix" the pose (location and orientation) of the ee_plaform. Essentially, I thought that Creo could solve the forward kinematics problem. However, this is what I see:
- So far as the trailing constraints are concerned: if you fix the pose of the ee-platform and ask Creo to generate the valid lengths of the six cylinders (inverse kinematics), it does just fine.
- However, considering the forward kinematic problem: Creo will allow for 4 out of 6 prescribed leg-lengths to be specified and it will come up with a valid ee-platform pose. In other situations, you'll get a cryptic error message and maybe you'll have time to spend wondering why your mechanism is not working or try ball-joints vs coincident point-point connections with varying degrees of success.
So in conclusion, I just have to state that given a ~$1,500 / year of maintenance fee one should expect more - I think the software should tell you why it can't find a solution, show you the alternatives, etc... Furthermore, I just have the impression is that Dassault Systemes/Solidworks has done its work much better than PTC/Creo...